There is an urgent need for effective drugs that can slow or halt the progression of neurodegenerative diseases like Alzheimer's disease (AD) and Parkinson's disease (PD), and diabetes, including type I and type II. Majority of the approved medicines for these conditions treat the symptoms rather than modifying the progression or causes of pathogenesis. Cell death is a hallmark of both diabetes and neurodegeneration and presents an opportunity for therapeutic intervention. Cao & Kaufman, Antioxid. Redox Signal. 2014, 21, 396-413. Beta cell death is an accepted major causal feature of both types of diabetes. Cnop et al., Diabetes 2005, 54, S97-107. Neuron death is also the major cause of cognitive decline in Alzheimer's disease. Niikura et al., Curr. Neuropharmacol. 2006, 4, 139-147. Neuron death is also implicated in Parkinson's and Huntington's diseases. Anglade et al., Histol. Histopathol. 1997, 12, 25-31.
A major cause of the cell death seen in diabetes and neurodegenerative disorders is a condition known as endoplasmic reticulum (ER) stress. Ozcan et al., Annu. Rev. Med. 2012, 63, 317-328. This ER stress is caused by abnormal calcium homeostasis, often caused by compromised function of the ER calcium pump, sarco/endoplasmic reticulum calcium ATPase (SERCA). Krebs et al., Biochem. Biophys. Res. Commun. 2015, 460, 114-121. Thus, an alternative approach to the treatment of neurodegeneration and diabetes is to target aberrant calcium signaling cascades that prove to be pathogenic. Stabilization of calcium signaling targets a pathogenic mechanism that is tied to many major features and risk factors of neurodegenerative diseases and diabetes. Rather than targeting a single endpoint this strategy aims to normalize calcium dyshomeostasis that has been recognized as a pathogenic accelerant in these diseases. Wang et al., J Cell Biol. 2012, 197, 857-867.
The ER is an organelle, which plays an essential role in multiple cellular processes that are central for cell survival and normal cellular functions. Those vital cellular processes include intracellular calcium homeostasis, protein secretion, and lipid biosynthesis. Anelli et al., EMBO J. 2008, 27, 315-327; Pizzo et al., Trends Cell Biol. 2007, 17, 511-517; Ma et al., J. Chem. Neuroanat. 2004, 28, 51-65.
Proper ER function and cellular health is dependent on the maintenance of a precise intracellular calcium balance of low cytosolic Ca2+ ion concentration coupled with high ER Ca2+ ion concentration. La Rovere, et al., Cell Calcium 2016, 60, 74-87; Rizzuto, et al. Nat. Rev. Mol. Cell Biol. 2012, 13, 566-578; Reddish, et al. Int. J. Mol. Sci. 2017, 18, 1024. Numerous diseases are associated with aberrant calcium homeostasis and transport. Mekahli, et al., Cold Spring Harb. Perspect. Biol. 2011, 3, a004317.
Perturbation of ER homeostasis leads to accumulation of unfolded protein in the ER, triggering an evolutionarily conserved response known as the unfolded protein response (UPR). Ron et al., Nat. Rev. Mol. Cell Biol. 2007, 8, 519-529; Malhotra et al., Semin. Cell Dev. Biol. 2007, 18, 716-731. Disturbances that lead to ER stress include, for example, disturbances in cellular redox regulation, glucose deprivation, aberration of calcium regulation in the ER, viral infection, high-fat diet, protein-inclusion-body diseases (e.g., chronic neurodegenerative diseases), and inclusion-body myositis. Kim et al., Nat. Rev. Drug Dis. 2008, 7, 1013-1030; Ma et al., J. Chem. Neuroanat. 2004, 28, 51-65; Ozcan et al., Science 2004, 306, 457-461; Frand et al., Trends Cell Biol. 2000, 10, 203-310. ER stress has been linked to a wide range of diseases, including neurodegeneration (e.g., Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, polyglutamine disease, and prion disease), stroke, bipolar disorder, heart disease, atherosclerosis, cancer, diabetes (types 1 and 2), muscle degeneration, inflammatory diseases, and autoimmune disease. Kim et al., Nat. Rev. Drug Dis. 2008, 7, 1013-1030; Oyadomari et al., Cell Death Differ. 2004, 11, 381-389.
Sarcoplasmic/endoplasmic reticulum Ca2+ ATPase (SERCA), is a major regulator of ER stress and glucose homeostasis in obesity. Park et al., Proc. Natl. Acad. Sci. U.S.A. 2010, 107, 19320-19325. Obesity disrupts intracellular Ca2+ homeostasis and induces ER stress. Fu et al., Nature 2011, 473, 528-531. Chronic activation of ER stress has been implicated in the development of insulin resistance and diabetes in obesity. Hotamisligil, Cell 2010, 140, 900-917; Kim et al., Nat. Rev. Drug Discov. 2008, 7, 1013-1030. Restoration of SERCA expression in the liver of diabetic mice either via gene therapy or pharmacological activation reduced ER stress and improved the diabetic phenotype. Kang, et al., J Biol. Chem. 2016, 291, 5185-5198; Park, et al., Proc. Natl. Acad. Sci. U.S.A. 2010, 107, 19320-19325. Restoration of Ca2+ homeostasis via SERCA activation has been shown to alleviate dyskinesia in a model of Parkinson's disease. Dahl, Bioorg. Med. Chem. 2017, 25, 53-57. SERCA activation has also been shown to improve memory and coordination in a transgenic mouse model of Alzheimer's disease. Krajnak & Dahl, Bioorg. Med. Chem Lett. 2018, 28, 1591-1594. Therefore, there is a need for therapeutic agents capable of reducing ER stress or restoring ER calcium homeostasis for treating diabetes and neurodegeneration.